The cloud point meter is a measuring instrument for measuring the temperature at which a petroleum product begins to cloud as a result of deposition of paraffin wax contained in the petroleum product when the petroleum product such as gas oil is cooled under a predetermined condition. The phenomenon of deposition of solid matters is not limited to the petroleum product, which is also observed in the same manner at a relatively low temperature for many chemical products such as plasticizers and surface active agents. Therefore, in order to evaluate the quality of these products, it is extremely important to accurately measure the cloud point.
Japanese Industrial Standard (JIS) K 2269 specifies the method for testing the pour point of crude oil and petroleum products and the cloud point of petroleum products. According to the test method as described above, a certain amount of a sample is prepared, and it is maintained at a temperature higher than an expected cloud point by not less than 14.degree. C. The sample is placed in an outer tube of a cooling bath so that the sample is allowed to arrive at a temperature in the vicinity of the expected cloud point. After that, the sample is taken out every time when the temperature of the sample is lowered by 1.degree. C. to investigate whether or not any cloud appears at the bottom portion of the sample. This operation is laborious, and it takes a long time to perform the measurement. For this reason, it is approved to use an automatic cloud point meter on condition that a result obtained by using the automatic cloud point meter can be confirmed to be not significantly different from a result obtained by using the specified test method, in accordance with JIS Z 8402.
For example, Japanese Laid-Open Patent Publication No. 61-17941 discloses a cloud point meter having a structure comprising a sample vessel for pouring a liquid sample thereinto and a pair of optical fibers connected to a light-projecting unit and a light-receiving unit, the pair of optical fibers being installed in the sample vessel, wherein a projecting light beam outgoing from one of the optical fibers and passing through the sample is reflected by a mirror surface disposed at the bottom surface of the vessel, and a reflected light beam is received by the other optical fiber. In this apparatus, any cloud is allowed to appear at the bottom surface of the vessel by cooling the sample. The cloud point of the sample is determined by observing rapid change in amount of received light coming from the bottom surface.
The present applicant has disclosed an automatic apparatus for measuring the cloud point in International Publication No. WO 94/24544. This apparatus has a sensor including, on a substrate, a laminate of a waveguide assembly comprising a light-introducing optical path and a light-emitting optical path which intersect with each other at a detecting surface to make contact with a test liquid, and a means for heating and cooling the test liquid. The angle of incidence and the angle of reflection of light with respect to the test sample are adjusted to give angles at which total reflection is caused by a deposit such as paraffin generated in the sample, at the detecting surface for the light-introducing optical path and the light-emitting optical path. When the test liquid is gradually cooled, the incoming light beam is refracted at the detecting surface to go toward the test liquid before arrival at the cloud point of paraffin. However, upon arrival at the cloud point, total reflection occurs at the detecting surface as a result of deposition of a solid matter of paraffin. The totally reflected light beam is detected by the aid of an optical fiber connected to the light-emitting optical path. Namely, this apparatus detects the deposition of a solid matter on the basis of the on/off system for the totally reflected light beam coming from the solid matter, wherein the temperature upon the detection is read to determine the cloud point.
The present applicant has also disclosed, in Japanese Patent Application No. 07-068979, a cloud point meter having approximately the same arrangement as that of the cloud point meter disclosed in International Publication No. WO 94/24544. The cloud point meter comprises a concave detecting area formed by an area including a point of intersection between a light-introducing optical path and a light-emitting optical path of a waveguide path, of a contact surface with respect to a test liquid. This cloud point meter is operated as follows. Namely, when deposited fine particles are generated in the detecting area as a result of cooling for the sample, the incoming light beam is optically scattered by the fine particles. The light beam is introduced into the light-emitting optical path, and it is detected by an optical fiber for the outgoing light beam. This cloud point meter makes it possible to quickly and accurately measure the cloud point by sensing and detecting the appearance of initially formed fine particles.
The cloud point meter concerning the conventional technique as described above greatly shortens the time required for measurement, as compared with the measuring method specified in JIS K 2269. However, it is demanded to provide a cloud point meter which makes it possible to more quickly and more accurately measure the cloud point.
An object of the present invention is to provide a novel method for measuring the deposit point (deposition point), which makes it possible to quickly and accurately measure the deposit point such as the cloud point. Another object of the present invention is to provide a deposit point meter which makes it possible to quickly and accurately measure the deposit point, and which can be easily produced.